Magnet



,July 16, 1929 P. l..4 JENSEN 1,721,0'

MAGNET File-d Oct. 26, 1927 PETE@ JENSEA y am 62W ws A {Toe/vsn slidableto lvary Patented July 16,1929.

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:PETER JENSEN, 0F ALAMEDA, CALIFORNIA, ASSIGN OR TO KARL JENSEN, 0F

PIEDMONT, CALIFORNIA.

MAGNET.

Application led October 26, 1927. Serial No. 228,807.

` My invention relates to magnetic sound reproducers. and particularlyto those of the electro-dynamic or moving coil type.

An object of my invent-ion is to produce an intense and uniform magneticfield in which to suspend the coil.

Another object of my invention is to pr0- duce such a field with aminimum of exciting energy.

A further object of `my invention is to provide a magnet havingan'annular air gap of uniform and accurate dimensions.

A still further object is to provide a ready means of adjusting andequalizing such an air gap.

My invention possesses other objects and valuable features, some ofwhich will be set forth in the following description of my inventionwhich is illustrated in the drawings forming part 0f the specification.It is to be understood that I do not limit myself to the showing made bythe said description and drawings, as I may adopt varying forms of myinvention within the scope of the claims.

Referring to the drawingsz Fig. 1 is a sectional view of a loud speakingtelephone 'embodying my invention` in a preferred form. The plane ofsection intersects the longitudinal axis of the device.

Y Fig. 2 is a fragmentary view, partly in "section, showing the use ofthe annular gage in adjusting the air gap. v

iroadly considered, my invention comprises a magnet having pole pieceswhich are so disposed as to form an air gap between them. The portionsof the magnet carrying the two pole surfaces are mutually theconfiguration of the gap, and once adjusted, may be clamped to preventfurther relative movement.

Sound cproducers of the electro-dynamic or moving coil type comprise amagnet which provides a powerful magnetic field.

L ving within this field, and at right angles' to the lines of forceforming it is'suspended a .coil which carries .the telephonie currentrepresenting the sound to be reproduced. This telephonie current sets upa magnetic feld'of its own, which reacts with themain field to urgethecoil in a direction normal toboth field and coil.

If the coil be fixed to a suitable radiatinzia;`

system its energy will be delivered to the air. The designof such adevice is directed to the end that this energy be so delivered aseflicientlyas possibleand that it follow, as closely as may be, theexact wave form of the electrical energy supplied.

The force acting on the coil at any instant is proportional to theproduct of the constant field times the current in the movable coil. It-is evident therefore that other things being equal, the sensitivity vofthe device is directly dependent upon the strength of the field.

-If the magnet is properly designed only a very small proportion of thelmagnetomotive force is' expended in the ferro-magnetic portions of thecircuit, the major part ofA the force going to maintain the field in the'air ap.

e magnetomotive force necessary to produce a given strength of field inthe gap is directly proportional to the gap length. It can thereforereadily be seen ythat it is desirable to make the'part of the gap notactually occupied by the coil, just as short i as possible, i. e., toreduce clearances to a minimum. At the-Sametime the coil must be whollyfree from the sides of the gap, for

friction at this point Will produce/serious distortion if it does notentirely revent the reproducer from functioning\ ence a reproducer ofthis character, to be `commercially practical, must be so designed thatvthe parts may be held to tolerances of the orderof one thousandth of aninch, and means must be provided foraccurately coil and air gap so thatthe coil is freely movable in its designed direction of motion, but ispositively prevented from motion in other dimensions. How I` accomplishthis in a. preferred embodiment of my invention will now be set fort-hin detail.

The main or constant field is provided by positioning awinding 6 lwhichI have shown insulated from a brass bobbin 7 by a layef 8 of fibrousmaterial. Surroundig the winding is thel ferro-magnetic casing 9,provided at its lower end with the inwardly projecting flange 11 whichconstitutes oneportion 'of the yoke. A plate,12 constituting theremainder. of the yoke is attached to the flange by the screwsI 13 whichare threaded into the flange. The holes in the plate thru which thesescrews pass are sufficiently large to allow an adjusting movement of theplate' in its own plane of several thousandths of an inch when thescrews. are loose.y

`VRiveted or otherwise rigidly fixed to the plate 12 is the core 14which isfloosely encircled by the liange. 11 and projects completelythru the coil.' The free end of thisl core or stud forms one of the polepieces defining the air gap. The other pole piece ils `formed by thering 16 which is accurately positioned on the casing by a groove orr'abbet formed in its periphery. l

A lframe 17, preferably of Lcast aluminum, is secured to the ring -polepiece by the screws 18. Lugs `19, cast integral with `the frame arefastened to the brackets 21 by the Screw .22, and the brackets, inlturn, are screwed to the casing, thus holding the pole piece,4togetherkwith the frame and the parts attached thereto, lirmly'in placerIt is advantageous to have the screws 23, which'securevthe brackets to:the casing, pass completely thruy the latter, and impinge` upon theflange ofthe bobbin 7, thus preventing it fromshifting in ship-ment orotherwise.

'Mounted 'upon the frame are the movable elements ofthe reproducer.These comprise the coil 24=`which is wound upon and cemented to the form26. This form may be turned from' a suitable material such as bakes liteor Wound from paper, with a thickened portion' provided at its outerend. The conical diaphragm 27 is truncated and is serrated from theplane at which its inner .diameter is equal to,l the outer diameter Aofthe .form, the` serrations being` bent outward1 to form `a projectingiiange which embraces and conforms tothefthickened portion of the form.

Overl the junction thus formed is pressed i a spider 28 -which comprisesa collar with projecting spiral spokes. The spider preferably is punchedfrom thin sheet metal, the portion forming the collar being drawnperpendicular to the plane -of the'spokes. Be- 4fore assembly theadjacent surfaces of collar, form and diaphragm are coated with lacqueror cement, which holds the parts perfmanently in place. A The spider issecured to the Vframe by screws'29 passing thru the outer ends of thespokes and clamping them between the washers 31, which are preferably offibrous mate- A rial. The leads from thel coilf24 are secured to thespokes, preferably by .ceinb thereto betweerl layers of thin insulation,fthis construction preventing vlthe breakage of the leads from theconstant vibration to which they are subjected, which is a `serioussourcev ofI failure in reproducers of this type. Suitable means areprovided at the distal portionof the frame 17 for flexibly supportingvthe diaphragm 27. ince this'is no part of the present invention, itneed not be shown or described herein. Y

The construction just described ermits the yready and accuratepositioning o all of theV parts. `The magnet structure is first assemnting theml piece, the yoke portions 11 and 12 sliding to`| allow thestud to center accurately to permit this. Screws" 13 are theny tightenedand the gage withdrawn.

The ring pole 16 and frame 17 are drilled in jigs, so that when thespider 28 is screwed in place the coil 24 is'l centeredvin the gapwithout further adjustment. The spokes of the spider, being spirallydisposed, allow a considerable movement of the coil thru'the gap, buteffectually. prevent motion across the gap which would permit the coilto strike the pole pieces.

' It is of' courseto be understood that in claiming the magnetic circuitcomprising thestud pole 14, yoke 11, 12, casing 9 and ring pole `16 asbeingferro-magnetic I do notlim it 'myself to iron, but include any ofthe metals or alloys having a permeability materially higher thanv air.

1. An electro-magnetJ comprising a winding, a ring pole piece adjacentthe winding, and a stud-pole adjacent the winding and projecting intothe ringl pole piece, said pole pieces being mutually slidable forvarying the gap between their adjacent faces. A

2'. An electro-magnet comprising a winding, a ring pole piece 'adjacentthe winding, -a stud pole adjacent thev winding-and adjacent the ringpole piece, and mutually adjustable yokes upon which .the pole piecesare mounted.

3. A magnet comprising a ring p ole pice, and a stud pole pieceprojecting into the ring pole piece, said pole pieces being mutuallyslidable for varying the gap betweentheir adjacent portions.

4. An electro-magnet comprising a winding, a stud pole piece within thewinding, a ringpole piece adjacent one end of the Winding andsurrounding a portion of the stud pole piece, a casing surrounding thewinding and carrying the-ring pole piece, and ayoke 'fixed to the studpole piece and adjustable on said casing to vary the co-nfiguration ofthe gap between v the pole pieces. y e

v 5. An electromagnet comprising a winding, a stud pole piece within thewinding,

a ring pole piece adjacent one end of the i.

winding and surrounding a portion of. the

stud Ipole piece,y a casing having an internally extending flange andsurrounding the winding and carrying the ring pole piece, and a yoke xedto the stud pole vpiece and adjustable on said flange to vary theconfigurationpieces.

`of the gap between the. pole-l 6. A magnet comprising a casing carryingav pole piece, a second polel piece within the casmg. and means externalto the casing for varying the configuration of the gap between said polepieces transversely .of said i casing.

7. A magnet comprising a caslng` a rmg lpole piece mounted von theeasing, a stud pole piece within the caslng, and means external to theeasing for varying the `conJ figuration of the gap between said pole ingthe ring pole piece. and a yoke fixed to the stud pole piece andadjustable on said flange to vary the configuration of the gap betweensaid pole pieces.

9. An electro-magnet omprising a winding, a stud pole piece within thewinding. a ring pole piece adjacent one end of `the winding andsurrounding a :portion of the stud pole piece,`a casing surrounc'lingthe winding and carrying one of said pole pieces, tl1e other of saidpole pieces being adjustable on said casing to vary the. cniguration ofthe gap.

`10. An electro-magnet comprising a.' winding, a stud pole piece withinthe winding, a ring pole piece adjacent -one end of the winding andsurrounding a portion of the stud pole piece, a Casing surrounding thewinding and carrying one of said pole pieces and having a flange onrwhiclithe other of said pole pieces is adjustable to vary vtheconfiguration of said gap.

,In testimony whereof, I

Y have hereunto set my hand.

